It is desirable to have underwater marine coatings that deter fouling by marine organisms through non-toxic means. One approach to solving this problem is by preparing fouling-release coatings. Fouling-release coatings do not suppress the settlement of fouling organisms through chemical means, such as biocides. Instead, organisms can only form a weak adhesive bond to the coating and are thus easily dislodged by shear forces.
Coatings based on crosslinked poly(dimethysiloxane) (PDMS) elastomers have low surface energy and may function as fouling-release coatings. Several such systems are available commercially. PDMS elastomers suffer from many disadvantages such as their poor adhesion to many substrates. PDMS elastomers are also mechanically weak and easily damaged. In addition, while many marine organisms such as barnacles, tubeworms, etc. cannot easily adhere to PDMS elastomers, other organisms, such as diatoms, can adhere well, resulting in the formation of undersirable “slimes” on PDMS coatings.
It has been recognized in the research community that poly(ethylene oxide) (PEO) and zwitterionic based materials are commonly used as protein resistant materials. Chang et. al. “Highly Protein-Resistant Coatings from Well-Defined Diblock Copolymers Containing Sulfobetains,” Langmuir, 2006, Vol 22, pp. 2222-2226, designed diblock copolymers with fixed polypropylene backbones and a range of chain lengths of polysulfobetaine poly(SBMA) synthesized via atom transfer radical polymerization (ATRP). The copolymers were absorbed on to methyl (CH3)-terminated self-assembled monolayers (SAM) and nonspecific protein absorption was compared. In another study done by Cheng et. al., “Inhibition of Bacterial Adhesion and Biofilm Formation on Zwitterionic Surfaces,” Biomaterials, 2007, 28, 4192-4199, long chain poly(SBMA) were grafted on to SAMs via ATRP and studied for long term and short term protein adsorption as well as biological evaluation of SAMs surface properties over time. It was found that the longer chain length of the zwitterionic moiety greatly affected the reduction of protein adsorption due to surface packing. However, SAMs are not suitable for use as durable coatings because SAMs are difficult to prepare and fail to have any long-term durability.
Amphiphilic compounds are designed to have both hydrophobic and hydrophilic moieties on one compound. These compounds have gained popularity for applications involving non-fouling biomaterials based on the idea that surfaces with amphiphilic compounds will form nanoscale heterogeneities, thus creating a surface topography that is unsuitable for the proliferation and adsorption of proteins and marine micro-foulers.
It is challenging to design a practical coating system for underwater use that contains either PEO or poly(SBMA). Typically, the coating is too hydrophilic and swells excessively when immersed in water. Excessive swelling results in a coating that has poor mechanical properties, thus not providing the durability needed for the coating application.
A self-stratified siloxane-polyurethane coating system has been shown to have good fouling-release properties. The low surface energy of PDMS is obtained, while the bulk properties are that of polyurethane. Pieper et al., “A Combinatorial Approach to Study the Effect of Acrylic Polyol Composition on the Properties of Crosslinked Siloxane-Polyurethane Fouling-Release Coatings,” Journal of Coatings Technology and Research, 2007, Vol. 4, No. 4, pp. 453-461, studied siloxane-urethane coatings containing aminopropyl terminated poly(dimethylsiloxane) (APT-PDMS), an acrylic polyol, and an aliphatic isocyanate. These materials were selected for their physical, mechanical and fouling-release performance properties. The results of the study were explained by the self-stratifying mechanism in which the low surface energy PDMS preferentially migrates to the surface of the coating while the bulk of the coating remains as the acrylic polyurethane. The fouling release properties of some of the coatings were good for the green macroalga Ulva sporelings but only slightly improved for the Navicula diatoms when compared to standard silicones.
It is an object of the present invention to prepare zwitterionic/amphiphilic pentablock copolymers.
It is another object of the present invention to prepare polyurethane coatings from the zwitterionic/amphiphilic pentablock copolymers such that the polyurethane coatings having anti-adherent properties.
It is another object of the present invention to prepare anti-fouling marine coatings from zwitterionic/amphiphilic pentablock copolymers which are easy to prepare and have long-term durability.